1. Field of the Invention
The invention is polyamide-based molding resin with high impact resistance, the process for its preparation, and the molded resin product.
2. The Prior Art
Polyamide resins have long been known for their excellent toughness, flexibility, abrasion resistance and relatively high impact strength. Molded or extruded polyamides have found application in appliances, consumer products, electronics, machine components, automotive parts, gears, and like uses.
While the impact strength of polyamide resins is relatively high among molding resins, it is insufficient for use where extremely high impact strength is required, as in collision-vulnerable automotive body parts. Compared to steel, for example, even polyamide molding resins, modified as so far known in the prior art, fall far short of the necessary impact resistance to provide a meaningful entry into markets requiring such high impact strength.
Past efforts to modify properties of polyamide resins have included the forming of blends with other resinous materials which in themselves have certain desirable properties not inherent in the polyamides, and without sacrificing to any great extent the inherent physical properties of the polyamide. For example, among the attempts to improve impact strength were the blending of polyamides with graft or random copolymers of monoolefins and unsaturated carboxylic acids or acid esters, as disclosed in U.S. Pat. Nos. 3,236,914 and 3,472,916; and by forming blends of a polyamide, a polyolefin and an olefin-carboxylic acid copolymer as disclosed in U.S. Pat. No. 3,373,223. Some improvement in impact strength was obtained as described in U.S. Pat. No. 3,984,497 through the use of an alkyl acrylate elastomer with a polyamide. Some tear resistance has been added to polyamides, as taught in U.S. Pat. No. 3,546,319, by the use of up to 15% of an elastomer. None of these modifications of polyamides, either alone or in combination, have provided the high degree of impact resistance necessary to withstand impacts typical of minor automotive accidents.
Succinic anhydride functionality (as taught in U.S. Pat. No. 4,010,223) has been incorporated in elastomeric copolymers of ethylene, at least one non-conjugated diene and at least one C.sub.3 -C.sub.6 .alpha.-olefin (EPDM). An improvement in impact resistance has been obtained by using certain anhydride or succinic-functional polymers and elastomers to modify polyamides as is taught in NL No. 7,605,485.
To obtain improved impact resistance in a polyamide molding resin without a substantial sacrifice of other desirable properties of the resin with compositions not taught in the prior art would be a significant advance in the art and is an object of this invention.